Porous honeycomb filter and manufacturing method thereof

ABSTRACT

A porous honeycomb filter made from a material containing cordierite, of which pore distribution is controlled, as the primary crystalline phase. The pore distribution is such that the volume of a pore with a diameter of below 10 μm is 15% or less of the total pore volume, the volume of a pore with a diameter of 10 to 50 μm is 75% or more of the total pore volume, and the volume of a pore with a diameter of above 50 μm is 10% or less of the total pore volume. This porous honeycomb filter has a high collection efficiency for fine particles (particulates), or the like, and can prevent increase in pressure loss due to the plugging of pores, and particularly can exploit the characteristics thereof for diesel engines that use recent high-pressure fuel injection, common rails, etc.

TECHNICAL FIELD

The present invention relates to a porous honeycomb filter and amanufacturing method thereof, and more particularly to a poroushoneycomb filter that has a high efficiency in collecting fine particles(particulates) and the like. This porous honeycomb filter can prevent anincrease in pressure loss due to the plugging of pores, and it isespecially suitable for exploiting the characteristics thereof fordiesel engines that use recent high-pressure fuel injection, commonrails, etc. The invention also relates to a manufacturing methodthereof.

BACKGROUND ART

Porous honeycomb filters, having a structure in which a plurality ofthrough holes opened to the end surface of the exhaust gas flow-in sideand to the end surface of the exhaust gas flow-out side are alternatelysealed at both the end surfaces, have recently been used as apparatusesfor removing particulate in exhaust gas. In these porous honeycombfilters the exhaust gas that flows in at the exhaust gas flow-in sideend surface is forced to pass through partition walls (having aplurality of pores) between through holes to thereby collect and removeparticulate in exhaust gas.

In this porous honeycomb filter, the pore distribution needs to becontrolled because performance figures such as collection efficiency andpressure loss vary depending on the diameter of the pores formed onpartition walls between through holes in relation to the size ofparticulates in the exhaust gas.

Traditionally, a porous honeycomb filter made from cordierite, which isexcellent in heat resistance, or from silicon carbide, which isfrequently used. For porous honeycomb filters made from silicon carbide,of which pore diameter is easily controlled, a filter with an averagepore diameter of 1 to 15 μm and the pore diameter thereof beingcontrolled with the standard deviation (SD) of as extremely narrow arange as 0.20 or less in the pore distribution, has been disclosed(JP-A-5-23512).

On the other hand, for porous honeycomb filters made from cordieritewhere the pore diameter is controlled, a honeycomb filter has beendisclosed with an average pore diameter of 25 to 40 μm. It is obtainedby a manufacturing method in which the porosity is increased by notcausing kaolin and aluminum oxide to be contained in thecordierite-forming raw material and also by using a raw material made byadding a specified organic blowing agent or a flammable substance to acordierite raw material. The cordierite raw material is composed ofaluminium hydroxide (the powders with particle diameters of 0.5 to 3 μmand of 5 to 15 μm make up 50 to 100% of the whole of the aluminiumhydroxide), fused silica (average particle diameter of 30 to 100 μm) andtalc, of which particle diameter is controlled within a specified range,has been disclosed (JP-A-9-77573).

However, in this honeycomb filter, the pore diameter thereof isprimarily controlled by aluminium hydroxide and an organic blowing agentor a flammable substance, and so the average pore diameter was capableof being controlled, but the pore distribution was not capable of beingset in a desired narrow range. In addition, the aluminium hydroxide wasmade to become coarse particles, thereby causing the problem ofincreasing the coefficient of thermal expansion as well.

To the contrary, honeycomb filters made by a manufacturing method inwhich a raw material prepared by adding graphite as a pore-forming agentto a cordierite-forming raw material produced by making each componentof talc, silica, alumina and kaolin a powder of a specific particlediameter and then mixing them in specific contents, with poredistributions in which <1> the pores with a diameter of 2 μm or lessmakes up 7% by volume or less of the total pore volume, and <2> thepores with a diameter of 100 μm or more makes up 10% by volume or lessof the total pore volume have been disclosed, respectively, in JapanesePatent Nos. 2578176 and 2726616.

In these honeycomb filters, however, the difference in easiness ofcontrolling the pore diameter for each component was not taken intoconsideration, and therefore the lower limit or the upper limit of thepore distribution was only controlled at most and it was impossible toset the pore distribution in a desired narrow range.

To the contrary, a honeycomb filter where a pore with pore diameters of10 to 50 μm makes up 52.0 to 74.1% by volume of the total pores, isobtained by a manufacturing method in which, focusing on the differencein easiness of controlling the pore diameter for each component of talc,silica, alumina and kaolin, a cordierite-forming raw material isprepared by setting the powder with a particle diameter of 150 μm ormore to be 3% by weight or less of the whole raw material and alsosetting the powder with a particle diameter of 45 μm or less to be 25%by weight or less, for both talc and silica, has been proposed(JP-A-7-38930).

In this honeycomb filter, the pore diameter thereof is controlled in anarrow range of from 10 to 50 μm for the first time in a honeycombfilter made from cordierite. Compared with a variety of cordieritehoneycomb filters mentioned above, the filter can not only increasecollection efficiency, but also prevents an increase in pressure loss bythe prevention of plugging. In addition, the filter can lower thecoefficient of thermal expansion by decreasing the particle diameter ofthe talc contained in the filter.

However, particulates in exhaust gas have lately been made small andbeen homogenized (particle diameter of particulates is almost about 1μm) with decreasing emission as a result of improved diesel engines(high-pressure fuel injection, common rails, etc. are used), and thus ahoneycomb filter in which the pore diameter is extremely highlycontrolled has been strongly required.

On the contrary, while the aforementioned honeycomb filter has beenproduced, completely neglecting a close association of kaolin in acordierite-forming raw material with the formation of a pore of 10 μm orless, pores with a diameter of 10 to 50 μm cannot be formed at a highlevel of 75.0% by volume or more, so that recent demand cannot besatisfied.

The present invention has been made considering the aforementionedproblem, and the objects thereof are to provide a porous honeycombfilter that has a high efficiency in collecting fine particles(particulates) and the like and prevents an increase in pressure lossdue to the plugging of the pores, especially suitable for exploitingthese characteristics for diesel engines that use recent high-pressurefuel injection, common rails, etc., and also to provide a manufacturingmethod thereof.

DISCLOSURE OF THE INVENTION

The inventors, as a result of studies to solve the aforementionedproblem, have found out that the pore size distribution can be highlycontrolled in a desired range by regulating the particle diameter of thesilica component of a cordierite-forming raw material and also loweringthe concentration of the kaolin, and have completed the presentinvention.

In other words, the present invention provides a porous honeycomb filtermade from a raw material composed of cordierite as the primarycrystalline phase, of which the pore distribution is controlled,characterized in that, in the pore distribution, the volume of a porewith a diameter of less than 10 μm is 15% or less of the total porevolume, the volume of a pore with a diameter of 10 to 50 μm is 75% ormore of the total pore volume, and the volume of a pore with a diameterof above 50 μm is 10% or less of the total pore volume.

In a honeycomb filter of the present invention, the porosity of thehoneycomb filter is preferably 50 to 75%, more preferably 65 to 75%, andparticularly preferably 68 to 75%. In addition, the coefficient ofthermal expansion of the honeycomb filter is preferably 1.0×10⁻⁶/° C. orless at 40 to 800° C.

Further, the present invention provides a method of manufacturing aporous honeycomb filter, using a ceramic raw material primarily composedof a cordierite-forming raw material, in which the cordierite-formingraw material contains 10% by weight or less of kaolin and also has aparticle size distribution in which the raw material contains 1% byweight or less of a powder with a particle diameter of 75 μm or more ofsilica (SiO₂) source components except both kaolin and talc.

In the method of manufacturing a honeycomb filter of the presentinvention, the filter can contain 1 to 10% by weight of kaolin, incontrast to the manufacturing method described in Japanese PatentLaid-Open 9-77573.

In addition, silica (SiO₂) source components except both kaolin and talcpreferably contain at least one species of quartz and fused silica.

Furthermore, a cordierite-forming raw material preferably contains asalumina (Al₂O₃) source components at least one species of aluminiumoxide and aluminium hydroxide. In this case, the raw material preferablycontains as alumina (Al₂O₃) source components 15 to 45% by weight ofaluminium hydroxide with a particle diameter of 1 to 10 μm, or 0 to 20%by weight of aluminium oxide with a particle diameter of from 4 to 8 μm.

Additionally, a cordierite-forming raw material preferably contains 37to 40% by weight of talc as a magnesia (MgO) source component. In thiscase, the particle diameter of the talc is preferably 5 to 40 μm.

Further, a ceramic raw material preferably contains 1 to 4 parts byweight of foam resin with respect to 100 parts by weight of acordierite-forming raw material.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail in thefollowing.

1. Porous Honeycomb Filter

A porous honeycomb filter of the present invention is a porous honeycombfilter made from cordierite as the primary crystalline phase, of whichpore distribution is highly controlled in a specified range.

A detailed description will be given in the following.

A porous honeycomb filter of the present invention is made fromcordierite as the primary crystal and the cordierite may be selectedfrom any one form of oriented, unoriented, α crystalline, and βcrystalline forms, and the like.

In addition, the filter may contain other crystalline phases, includingmullite, zircon, aluminium titanate, clay bond silicon carbide,zirconia, spinel, indialite, sapphirine, corundum and titania.

Further, these crystalline phases may be contained as a single speciesor as two or more species at the same time.

In the pore distribution of a porous honeycomb filter of the presentinvention, the volume of a pore with a diameter of below 10 μm is 15% orless of the total pore volume, the volume of a pore with a diameter of10 to 50 μm is 75 to 100% of the total pore volume, and the volume of apore with a diameter of above 50 μm is 10% or less of the total porevolume.

When the volume of a pore with a diameter of 10 to 50 μm comes to beless than 75% of the total pore volume and the volume of a pore with adiameter of below 10 μm exceeds 15% of the total pore volume, a pressureloss is increased due to the plugging of pores. Further, when a catalystis made to attach to the filter, a pressure loss is increased due toplugging of pores caused by the catalyst. On the other hand, when thevolume of a pore with a diameter of 10 to 50 μm comes to be less than75% of the total pore volume and the volume of a pore with a diameter ofabove 50 μm exceeds 10% of the total pore volume, the efficiency incollecting particulates is decreased.

In particular, since particulates are made small and homogenized as aresult of recent improved diesel engines, it is difficult to increasethe collection efficiency for particulates in line with such improvementin diesel engines, unless the volume of a pore with a diameter of 10 to50 μm is as high as 75% or more of the total pore volume for highefficiency.

In a honeycomb filter of the present invention, from the viewpoint ofdecreasing pressure loss and increasing collection efficiency, theporosity is preferably 50 to 75%, more preferably from 65 to 75% andparticularly preferably 68 to 75%. In addition, in terms of improvingthermal shock resistance when in use at high temperature, thecoefficient of thermal expansion is preferably 1.0×10⁻⁶/° C. or less at40 to 800° C.

Although a honeycomb filter of the present invention normally has astructure in which a plurality of through holes opened to the endsurface of the exhaust gas flow-in side and to the end surface of theexhaust gas flow-out side are alternately sealed at both the endsurfaces, the shape of the honeycomb filter is not particularlyrestricted. For example, the filter may be a cylinder having endsurfaces with a shape of a circle or an ellipse, a prism having the endsurfaces with a shape of a polygon such as a triangle or a square, ashape in which the sides of these cylinder and prism are bent like an“doglegged shape,” or the like. In addition, the shape of through holesis not particularly limited. For example, the sectional shape may be apolygon such as a square or an octagon, a circle, an ellipse, or thelike.

Furthermore, a porous honeycomb filter of the present invention can bemanufactured by a method described below, or the like.

2. A Method of Manufacturing a Porous Honeycomb Filter

A method of manufacturing a porous honeycomb filter of the presentinvention is a method of manufacturing a porous honeycomb filter using aceramic raw material made from a primary raw material of acordierite-forming raw material, in which the contents and particlediameters of specific components in a cordierite-forming raw materialare controlled in specified ranges.

Detailed descriptions will be given in the following.

A cordierite-forming raw material used in the present invention has aparticle size distribution in which the raw material contains 1% byweight or less of a powder with a particle diameter of 75 μm or more ofsilica (SiO₂) source components except both kaolin and talc, or morepreferably 0.5% by weight or less.

As a result, pores with a narrow diameter range of 10 to 50 μm can beformed in an extremely high yield and a honeycomb filter having a highcollection efficiency and exhibiting no increase in pressure loss due toplugging of pores can be manufactured.

In other words, the present invention has found out that silica (SiO₂)source components except both kaolin and talc in a cordierite-formingraw material, which are different from other components, can form poresof diameters substantially corresponding to the particle sizes ofcomponents, and that, noticing that the silica source components rarelyparticipate in forming a pore with a diameter of 10 μm or less, poreswith a narrow diameter range of 10 to 50 μm can be formed in anextremely high yield by removing a coarse powder with a diameter of 75μm or more.

Silica (SiO₂) source components except both kaolin and talc includequartz, fused silica and mullite. Of them, at least one species ofquartz and fused silica is preferably contained because they stablyexist to high temperature during firing and pore diameters thereof areeasily controlled.

A cordierite-forming raw material preferably contains 15 to 20% byweight of these silica (SiO₂) source components. In addition, Na₂O, K₂O,etc. may be contained as impurities, and the total content of theseimpurities in silica (SiO₂) source components is preferably 0.01% byweight or less because containing these impurities can prevent anincrease in the coefficient of thermal expansion.

A cordierite-forming raw material used in the present invention shouldfurther contain 10% by weight or less of kaolin.

When the content of kaolin exceeds 10% by weight, the formation of apore with a diameter of less than 10 μm cannot be controlled, so that itbecomes impossible to set the volume of a pore with a diameter of from10 to 50 μm to be 75% or more of the total pore volume even though theparticle sizes of the aforementioned silica (SiO₂) source componentsexcept both kaolin and talc are controlled.

That is, in the present invention, in addition to the control of theparticle size distribution of the aforementioned silica (SiO₂) sourcecomponents, noticing that the kaolin in a cordierite-forming rawmaterial mainly participates in forming a pore with a diameter of lessthan 10 μm, the formation of the pore with a diameter of less than 10 μmhas been found to be able to be almost controlled by decreasing thecontent of kaolin to 10% by weight or less.

Additionally, in the present invent, since the content of kaolin isconstrained by controlling the pore distribution, kaolin may becontained in the range of from 1 to 10% by weight, in contrast to themanufacturing method described in JP-A-9-77573.

In addition, although kaolin may contain mica, quartz, etc. asimpurities, containing these impurities can prevent an increase in thecoefficient of thermal expansion, and so the content is preferably 2% byweight or less.

Because each component for a cordierite-forming raw material used in thepresent invention is formulated to prepare a cordierite crystal with atheoretical composition, in addition to both the aforementioned silica(SiO₂) source components and kaolin, for example, magnesia (MgO) sourcecomponents such as talc and alumina (Al₂O₃) source components such asaluminium oxide and aluminium hydroxide need to be formulated.

As alumina (Al₂O₃) source components, one or both species of aluminiumoxide and aluminium hydroxide, which have few impurities, are preferablycontained, and particularly aluminium hydroxide is preferably contained.

In addition, some particle sizes of alumina (Al₂O₃) source componentscan lower the coefficient of thermal expansion and also can preciselycontrol the pore size distribution by means of the particle sizedistribution of the aforementioned silica (SiO₂) source components, andthus the particle diameter of aluminium hydroxide is preferably 1 to 10μm and the particle diameter of aluminium oxide is preferably 4 to 8 μm.

Furthermore, for alumina (Al₂O₃) source components, a cordierite-formingraw material preferably contains 15 to 45% by weight of aluminiumhydroxide and preferably contains 0 to 20% by weight of aluminium oxide.

Magnesia (MgO) source components, for example, include talc andmagnesite and particularly talc is preferably contained. Acordierite-forming raw material preferably contains 37 to 40% by weightof talc. The particle diameter of talc, which lowers the coefficient ofthermal expansion, is preferably 5 to 40 μm, more preferably 10 to 30μm.

In addition, magnesia (MgO) source components such as talc used in thepresent invention may contain impurities, including Fe₂O₃, CaO, Na₂O andK₂O.

However, the content of Fe₂O₃ in magnesia (MgO) source components ispreferably 0.1 to 2.5% by weight. A content in this range can lower thecoefficient of thermal expansion and can also provide a high porosity.

In addition, containing CaO, Na₂O and K₂O lowers the coefficient ofthermal expansion, and so the total content thereof in magnesia (MgO)source components is preferably 0.35% by weight or less.

The manufacturing method of the present invention can increasecollection efficiency and also decrease pressure loss by furtherincreasing porosity, and thus a cordierite-forming raw materialpreferably contains as an additive a pore-forming agent, or the like forforming pores.

Pore-forming agents, for example, include foam resins such as acrylicmicrocapsules, graphite, flour, starch, phenolic resin, poly(methylmethacrylate), polyethylene, and poly(ethylene terephthalate) andexpanded foam resins such as acrylic microcapsules are preferable.

Expanded foam resins such as acrylic microcapsules are hollow and thuscan, in a few amount, provide a honeycomb filter of a high porosity andcan restrain heat liberation of a pore-forming material in a firingstep, thereby lowering heat liberation in the firing step and decreasinggeneration of thermal stress even when a honeycomb filter of a highporosity is prepared by adding a pore-forming material.

Of course, although addition of a large amount of foam resin makes theporosity of an obtained honeycomb filter extremely large, the intensityis decreased to cause the filter to be easily damaged during canning, orthe like. Accordingly, the content of foam resin is preferably 1.0 to4.0 parts by weight with respect to 100 parts by weight of acordierite-forming raw material, more preferably 1.5 to 3.0 parts byweight.

In the present invention, as necessary, other additives can becontained; for example, a binder or a dispersant for promoting thedispersion into the medium of fluid may be contained.

In addition, a binder includes hydroxypropylmethyl cellulose, methylcellulose, hydroxyethyl cellulose, carboxylmethyl cellulose, orpolyvinyl alcohol; a dispersant includes ethylene glycol, dextrin, fattyacid soap, or polyalcohol.

Further, each additive described above can be used singly or incombination of two species or more, depending on purpose.

In the present invention, nothing is limited except that the contentsand particle diameters of particular components in a cordierite-formingraw material are controlled in specified ranges. For example, ahoneycomb filter can be produced in the following manufacturing process.

First, with respect to 100 parts by weight of the aforementionedcordierite-forming raw material, 3 to 5 parts by weight of a binder, 2to 40 parts by weight of a pore-forming agent, 0.5 to 2 parts by weightof dispersant, and 10 to 40 parts by weight of water are charged andthen kneaded, and the compound is plasticized.

Second, molding of a raw material to be plasticized can be carried outby means of the extrusion method; the injection molding method; thecompression molding method; a method in which after a ceramic rawmaterial is molded in a cylindrical shape, the through hole is molded;or the like. Of them, the extrusion method, which easily permitscontinuous molding and causes a cordierite crystal to be orientedleading to low thermal expansion coefficient, is preferably used.

Third, drying of a raw molded article can be carried out by hot-airdrying, microwave drying, dielectric drying, reduced-pressure drying,vacuum drying, freezing drying, or the like. Of them, a drying step of acombination of hot-air drying and microwave drying or of hot-air dryingand dielectric drying is preferable in terms of being able to dry thewhole rapidly and homogeneously.

Finally, firing of a dried molded article, although depending on thesize of the dried molded article, is normally conducted preferably at atemperature of 1410 to 1440° C. for 3 to 7 hours. In addition, thedrying step and the firing step may be conducted continuously.

Examples of the present invention will be described in detail in thefollowing. However, the present invention is not limited to theexamples.

1. Evaluation Method

Honeycomb filters obtained in the examples and comparative examplesdescribed later were evaluated by the following methods.

(1) Pore Distribution and Average Diameter of Pores

Pore distributions and average diameters of pores were measured by amercury injection porosimeter manufactured by Micromeritics Corporation.

(2) Porosity

Porosity was calculated from the total pore volume, regarding theabsolute specific gravity of cordierite as 2.52 g/cc.

(3) Collection Efficiency

Exhaust gas with soot generated by a soot generator was passed through ahoneycomb filter prepared in each example or comparative example for aconstant time (2 minutes). After filtration, the soot contained in theexhaust gas was collected with a filter paper and then the weight (W¹)of the soot was measured. Also, exhaust gas with soot generated for thesame time was collected with a filter paper without being passed througha filter and then the weight (W²) of the soot was measured. Thusobtained weights (W¹ and W²) were substituted in the equation (1) belowto evaluate collection efficiencies.

(W ² −W ¹)/(W ²)×100  (1)

(4) Soot Collection Pressure Loss

First, to both end surfaces of a honeycomb filter obtained in eachexample or comparative example was pressed against a ring with an insidediameter φ of 130 mm and soot generated by a soot generator through thisring was flowed within the range of 130 mm φ of the honeycomb filter tocollect 10 g of soot.

Finally, air of 2.27 Nm3/min was flowed, with the soot collected onhoneycomb filter, and then the pressure difference upstream anddownstream the filter was measured to evaluate the pressure loss in astate in which the soot is collected.

EXAMPLES AND COMPARATIVE EXAMPLES Example 1

A cordierite-forming raw material was prepared by mixing talc (averageparticle diameter of 20 μm, 4% by weight of a powder with a particlediameter of 75 μm or more), fused silica B (average particle diameter of35 μm, 0.5% by weight of a powder with a particle diameter of 75 μm ormore), and aluminium hydroxide (average particle diameter of 2 μm, 0% byweight of a powder with a particle diameter of 75 μm or more), of theaverage particle diameters and particle size distributions as shown inTable 1, in the ratio of 37% by weight of the talc, 19% by weight of thefused silica B and 44% by weight of the aluminium hydroxide as shown inTable 2.

Then, as shown in Table 2, with respect to 100 parts by weight of thiscordierite-forming raw material, 20 parts by weight of graphite, 7 partsby weight of poly(ethylene terephthalate), 7 parts by weight ofpoly(methyl methacrylate), 4 parts by weight of hydroxypropylmethylcellulose, 0.5 parts by weight of potassium laurate soap and 30 parts byweight of water were charged and then kneaded, and the compound wasplasticized. This plasticized raw material was made to formcylinder-shaped puddle using a vacuum tug mill and then was charged intoan extrusion machine to form a honeycomb shape.

Then, the thus obtained molded article was dried by dielectric drying,absolute-dried by hot-air drying, and then the end surfaces were cut toa specified size.

And then, the through holes of the honeycomb-shaped, dried article werealternately sealed at both the end surfaces where the through hole open,using slurry made from a cordierite-forming raw material of a similarcomposition.

Finally, the article was fired at 1420° C. for 4 hours to give ahoneycomb filter with a size of φ144 mm×L 152 mm, 300 μm in partitionwall thickness and with the number of cells of 300 cells/inch².

Example 2

A honeycomb filter was obtained as in the case of Example 1, except thatin Example 2 quartz B (average particle diameter of 19 μm, 0.3% byweight of a powder with a particle diameter of 75 μm or more) was mixedinstead of fused silica B (average particle diameter of 35 μm, 0.5% byweight of a powder with a particle diameter of 75 μm or more).

Comparative Example 1

A honeycomb filter was obtained as in the case of Example 1, except thatin Comparative Example 1 fused silica A (average particle diameter of 40μm, 6% by weight of a powder with a particle diameter of 75 μm or more)was mixed instead of fused silica B (average particle diameter of 35 μm,0.5% by weight of a powder with a particle diameter of 75 μm or more).

Example 3

A honeycomb filter was obtained as in the case of Example 1, except thatin Example 3 a cordierite-forming raw material was prepared by mixingtalc (average particle diameter of 20 μm, 4% by weight of a powder witha particle diameter of 75 μm or more), kaolin (average particle diameterof 10 μm, 2% by weight of a powder with a particle diameter of 75 μm ormore), quartz D (average particle diameter of 5 μm, 0.1% by weight of apowder with a particle diameter of 75 μm or more), aluminium oxide(average particle diameter of 6 μm, 0.2% by weight of a powder with aparticle diameter of 75 μm or more) and aluminium hydroxide (averageparticle diameter of 2 μm, 0% by weight of a powder with a particlediameter of 75 μm or more), of the average particle diameters andparticle size distributions as shown in Table 1, in the ratio of 40% byweight of the talc, 1% by weight of the kaolin, 21% by weight of thequartz D, 19% by weight of the aluminium oxide and 19% by weight of thealuminium hydroxide as shown in Table 2, and except that with respect to100 parts by weight of the thus obtained cordierite-forming rawmaterial, 20 parts by weight of graphite, 10 parts by weight ofpoly(ethylene terephthalate), and 10 parts by weight of poly(methylmethacrylate) were added as pore-forming agents.

Example 4

A honeycomb filter was obtained as in the case of Example 1, except thatin Example 4 a cordierite-forming raw material was prepared by mixingtalc (average particle diameter of 20 μm, 4% by weight of a powder witha particle diameter of 75 μm or more), kaolin (average particle diameterof 10 μm, 2% by weight of a powder with a particle diameter of 75 μm ormore), quartz B (average particle diameter of 19 μm, 0.3% by weight of apowder with a particle diameter of 75 μm or more), aluminium oxide(average particle diameter of 6 μm, 0.2% by weight of a powder with aparticle diameter of 75 μm or more) and aluminium hydroxide (averageparticle diameter of 2 μm, 0% by weight of a powder with a particlediameter of 75 μm or more), of the average particle diameters andparticle size distributions as shown in Table 1, in the ratio of 40% byweight of the talc, 3% by weight of the kaolin, 20% by weight of thequartz B, 18% by weight of the aluminium oxide and 19% by weight of thealuminium hydroxide as shown in Table 2, and except that with respect to100 parts by weight of the thus obtained cordierite-forming rawmaterial, 20 parts by weight of graphite, 9 parts by weight ofpoly(ethylene terephthalate), and 9 parts by weight of poly(methylmethacrylate) were added as pore-forming agents.

Example 5

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 5, instead of quartz B (average particle diameter of 19 μm,0.3% by weight of a powder with a particle diameter of 75 μm or more) asshown in Table 1, quartz D (average particle diameter of 5 μm, 0.1% byweight of a powder with a particle diameter of 75 μm or more) was mixedas shown in Table 2, and except that with respect to 100 parts by weightof the thus obtained cordierite-forming raw material, 25 parts by weightof graphite, 5 parts by weight of poly(ethylene terephthalate), and 10parts by weight of poly(methyl methacrylate) were added as pore-formingagents.

Example 6

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 6, instead of quartz B (average particle diameter of 19 μm,0.3% by weight of a powder with a particle diameter of 75 μm or more) asshown in Table 1, quartz E (average particle diameter of 10 μm, 0.1% byweight of a powder with a particle diameter of 75 μm or more) was mixedas shown in Table 2, and except that with respect to 100 parts by weightof the thus obtained cordierite-forming raw material, 20 parts by weightof graphite and 4 parts by weight of poly(ethylene terephthalate) wereadded as pore-forming agents.

Example 7

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 7, instead of quartz B (average particle diameter of 19 μm,0.3% by weight of a powder with a particle diameter of 75 μm or more) asshown in Table 1, fused silica B (average particle diameter of 35 μm,0.5% by weight of a powder with a particle diameter of 75 μm or more)was mixed as shown in Table 2, and except that with respect to 100 partsby weight of the thus obtained cordierite-forming raw material, 20 partsby weight of graphite, 3 parts by weight of poly(ethyleneterephthalate), and 9 parts by weight of poly (methyl methacrylate) wereadded as pore-forming agents.

Example 8

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 8, instead of quartz B (average particle diameter of 19 μm,0.3% by weight of a powder with a particle diameter of 75 μm or more) asshown in Table 1, fused silica C (average particle diameter of 16 μm, 1%by weight of a powder with a particle diameter of 75 μm or more) wasmixed as shown in Table 2, and except that with respect to 100 parts byweight of the thus obtained cordierite-forming raw material, 10 parts byweight of graphite and 17 parts by weight of poly(methyl methacrylate)were added as pore-forming agents.

Comparative Example 2

A honeycomb filter was obtained as in the case of Example 4, except thatin Comparative Example 2, instead of quartz B (average particle diameterof 19 μm, 0.3% by weight of a powder with a particle diameter of 75 μmor more) as shown in Table 1, quartz A (average particle diameter of 20μm, 8% by weight of a powder with a particle diameter of 75 μm or more)was mixed as shown in Table 2, and except that with respect to 100 partsby weight of the thus obtained cordierite-forming raw material, 20 partsby weight of graphite, 7 parts by weight of poly(ethyleneterephthalate), and 9 parts by weight of poly(methyl methacrylate) wereadded as pore-forming agents.

Comparative Example 3

A honeycomb filter was obtained as in the case of Example 4, except thatin Comparative Example 3, instead of quartz B (average particle diameterof 19 μm, 0.3% by weight of a powder with a particle diameter of 75 μmor more) as shown in Table 1, quartz C (average particle diameter of 5μm, 3% by weight of a powder with a particle diameter of 75 μm or more)was mixed as shown in Table 2, and except that with respect to 100 partsby weight of the thus obtained cordierite-forming raw material, 20 partsby weight of graphite, 10 parts by weight of poly(ethyleneterephthalate), and 10 parts by weight of poly(methyl methacrylate) wereadded as pore-forming agents.

Comparative Example 4

A honeycomb filter was obtained as in the case of Example 4, except thatin Comparative Example 4, instead of quartz B (average particle diameterof 19 μm, 0.3% by weight of a powder with a particle diameter of 75 μmor more) as shown in Table 1, fused silica D (average particle diameterof 70 μm, 39% by weight of a powder with a particle diameter of 75 μm ormore) was mixed as shown in Table 2, and except that with respect to 100parts by weight of the thus obtained cordierite-forming raw material, 20parts by weight of graphite, 6 parts by weight of poly(ethyleneterephthalate), and 7 parts by weight of poly(methyl methacrylate) wereadded as pore-forming agents.

Example 9

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 4 a cordierite-forming raw material was prepared as shown inTable 2 by mixing the following species in the ratio of 40% by weight oftalc, 5% by weight of kaolin, 19% by weight of quartz B, 17% by weightof aluminium oxide and 19% by weight of aluminium hydroxide, and exceptthat with respect to 100 parts by weight of the thus obtainedcordierite-forming raw material, 20 parts by weight of graphite, 7 partsby weight of poly(ethylene terephthalate), and 7 parts by weight ofpoly(methyl methacrylate) were added as pore-forming agents.

Example 10

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 4 a cordierite-forming raw material was prepared as shown inTable 2 by mixing the following species in the ratio of 40% by weight oftalc, 10% by weight of kaolin, 17% by weight of quartz B, 16% by weightof aluminium oxide and 17% by weight of aluminium hydroxide, and exceptthat with respect to 100 parts by weight of the thus obtainedcordierite-forming raw material, 10 parts by weight of graphite, 8 partsby weight of poly(ethylene terephthalate), and 15 parts by weight ofpoly(methyl methacrylate) were added as pore-forming agents.

Comparative Example 5

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 4 a cordierite-forming raw material was prepared as shown inTable 2 by mixing the following species in the ratio of 40% by weight oftalc, 15% by weight of kaolin, 14% by weight of quartz B, 15% by weightof aluminium oxide and 16% by weight of aluminium hydroxide, and exceptthat with respect to 100 parts by weight of the thus obtainedcordierite-forming raw material, 20 parts by weight of graphite, 4 partsby weight of poly(ethylene terephthalate), and 9 parts by weight ofpoly(methyl methacrylate) were added as pore-forming agents.

Comparative Example 6

A honeycomb filter was obtained as in the case of Example 4, except thatin Example 4 a cordierite-forming raw material was prepared as shown inTable 2 by mixing the following species in the ratio of 40% by weight oftalc, 19% by weight of kaolin, 12% by weight of quartz B, 14% by weightof aluminium oxide and 15% by weight of aluminium hydroxide, and exceptthat with respect to 100 parts by weight of the thus obtainedcordierite-forming raw material, 20 parts by weight of graphite, 4 partsby weight of poly(ethylene terephthalate), and 7 parts by weight ofpoly(methyl methacrylate) were added as pore-forming agents.

Example 11

A honeycomb filter was obtained as in the case of Example 10, exceptthat in Example 11, 2.4 parts by weight of an acrylic microcapsule, or afoam resin, (trade name: F-50E, manufactured by Matsumoto Yushi-SeiyakuCo., Ltd.) was charged with respect to 100 parts by weight of acordierite-forming raw material without addition of graphite,poly(ethylene terephthalate) and poly(methyl methacrylate) aspore-forming agents as shown in Table 2.

Example 12

A honeycomb filter was obtained as in the case of Example 10, exceptthat in Example 12 a cordierite-forming raw material was prepared asshown in Table 2 by mixing the following species in the ratio of 40% byweight of talc, 0% by weight of kaolin, 21% by weight of quartz D, 16%by weight of aluminium oxide and 23% by weight of aluminium hydroxide,and except that with respect to 100 parts by weight of the thus obtainedcordierite-forming raw material, 10 parts by weight of graphite, 5 partsby weight of poly(ethylene terephthalate), 5 parts by weight ofpoly(methyl methacrylate), and 1.8 parts by weight of an acrylicmicrocapsule, or a foam resin, were added as pore-forming agents.

Example 13

A honeycomb filter was obtained as in the case of Example 10, exceptthat in Example 13 a cordierite-forming raw material was prepared asshown in Table 2 by mixing the following species in the ratio of 40% byweight of talc, 5% by weight of kaolin, 19% by weight of quartz B, 17%by weight of aluminium oxide and 19% by weight of aluminium hydroxide,and except that with respect to 100 parts by weight of the thus obtainedcordierite-forming raw material, 20 parts by weight of graphite and 2.8parts by weight of an acrylic microcapsule, or a foam resin, were addedas pore-forming agents.

Evaluation

In Examples 1 to 13, in which silica source components except bothkaolin and talc have a particle size distribution of 1.0% by weight orless of a powder with a particle diameter of 75 μm or more, a honeycombfilter in which the volume of a pore of over 50 μm is controlled to be10% or less of the total pore volume can be obtained; in this honeycombfilter as high a collection efficiency as 85% or more has beensuccessfully attained. In particular, in Examples 3 and 5, in whichsilica source components except both kaolin and talc have a particlesize distribution of 0.1% by weight or less of a powder with a particlediameter of 75 μm or more, a honeycomb filter in which the volume of apore of over 50 μm is controlled to be 2% or less of the total porevolume can be obtained; in this honeycomb filter as extremely high acollection efficiency as 94% or more has been successfully attained.

On the other hand, in Examples 1 to 4, in which silica source componentsexcept both kaolin and talc have a particle size distribution of above1.0% by weight of a powder with a particle diameter of 75 μm or more, ahoneycomb filter in which the volume of a pore of over 50 μm exceeds 10%of the total pore volume can be obtained; in this honeycomb filter thecollection efficiency has become as low as 75% or less.

In addition, in Examples 1 to 13, in which the content of kaolin is 10%by weight or less, a honeycomb filter in which the volume of a pore of10 μm or less is controlled to be 15% or less of the total pore volumehas been successfully obtained. When to this filter is mounted acatalyst, it is estimated that the plugging of pores due to a catalystis restrained, leading to a small pressure loss during soot collection.

On the other hand, in Comparative Examples 5 and 6, in which the contentof kaolin exceeds 10% by weight, a honeycomb filter in which the volumeof a pore of 10 μm or less exceeds 15% of the total pore volume has beenobtained. When to this filter is mounted a catalyst, it is estimatedthat pressure loss is large due to the plugging of pores by thecatalyst.

Further, in Examples 11 to 13, in which 1.8 to 2.8 parts by weight of afoaming agent is added with respect to 100 parts by weight of acordierite-forming raw material, a honeycomb filter with a porosity offrom 68 to 75% can be obtained. In these honeycomb filters, as highcollection efficiencies as 91% more have been successfully obtained andcollection pressure losses are 8.5 (KPa) or less, i.e., pressure loss issmall during soot collection.

Additionally, in Example 12, when a honeycomb filter was produced byaltering the amount of foam resin to be added to 3.2 parts by weight, ahoneycomb filter with a porosity of 80% has been obtained; however, thestructure strength is not sufficient.

TABLE 1 Raw material Content of a powder with Cordierite-forming Averageparticle a particle diameter of raw material diameter 75 μm or morecomponent (μm) (% by weight) Talc 20 4 Kaolin 10 2 Quartz A 20 8 QuartzB 19 0.3 Quartz C 5 3 Quartz D 5 0.1 Quartz E 10 0.1 Fused silica A 40 6Fused silica B 35 0.5 Fused silica C 16 1 Fused silica D 70 39 Aluminiumoxide 6 0.2 Aluminium hydroxide 2 0

TABLE 2 Raw material preparation composition (wt %) Cordierite-formingraw material Pore-forming agent Silica source component AluminiumAluminium Foam Talc Kaolin Content oxide hydroxide Graphite PET *1 PMM*2 resin *3 (% by (% by (% by (% by (% by (parts by (parts by (parts by(parts by No. weight) weight) Component weight) weight) weight) weight)weight) weight) weight) Example 1 37 0 Fused silica B 19 0 44 20 7 7 0Example 2 37 0 Quartz B 19 0 44 20 7 7 0 Example 3 40 1 Quartz D 21 1919 20 10 10 0 Example 4 40 3 Quartz B 20 18 19 20 9 9 0 Example 5 40 3Quartz D 20 18 19 25 5 10 0 Example 6 40 3 Quartz E 20 18 19 20 4 0 0Example 7 40 3 Fused silica B 20 18 19 20 3 9 0 Example 8 40 3 Fusedsilica C 20 18 19 10 0 17 0 Example 9 40 5 Quartz B 19 17 19 20 7 7 0Example 10 40 10 Quartz B 17 16 17 10 8 15 0 Example 11 40 10 Quartz B17 16 17 0 0 0 2.4 Example 12 40 0 Quartz D 21 16 23 10 5 5 1.8 Example13 40 5 Quartz B 19 17 19 20 0 0 2.8 Comparative 37 0 Fused silica A 190 44 20 7 7 0 example 1 Comparative 40 3 Quartz A 20 18 19 20 7 9 0example 2 Comparative 40 3 Quartz C 20 18 19 20 10 10 0 example 3Comparative 40 3 Fused silica D 20 18 19 20 6 7 0 example 4 Comparative40 15 Quartz B 14 15 16 20 4 9 0 example 5 Comparative 40 19 Quartz B 1214 15 20 4 7 0 example 6 *1 PET: Poly(ethylene terephthalate) *2 PMM:Poly(methyl methacrylate) *3 Foam resin: Acrylic microcapsule

TABLE 3 Characteristics Coefficient Average pore of thermal CollectionCollection Pore distribution (%) diameter expansion pressure lossefficiency No. Porosity (%) to 10 μm 10 to 50 μm over 50 μm (μm) (×10⁻⁶/° C.) (KPa) (%) Example 1 60 2 89 9 26 0.6 9.4 86 Example 2 62 2 917 22 0.7 8.9 88 Example 3 65 5 93 2 17 0.6 8.7 94 Example 4 63 5 88 7 210.7 9.0 87 Example 5 65 10 88 2 16 0.6 8.5 95 Example 6 54 7 90 3 19 0.610.4 93 Example 7 58 7 85 8 23 0.6 9.9 87 Example 8 55 13 77 10 20 0.510.2 85 Example 9 61 8 86 6 20 0.7 9.1 89 Example 10 59 15 80 5 19 0.79.2 90 Example 11 68 15 75 10 21 0.9 8.5 91 Example 12 72 12 82 6 18 0.97.8 98 Example 13 75 8 82 10 25 1.0 7.4 96 Comparative 60 2 83 15 28 0.69.4 71 example 1 Comparative 62 4 79 17 22 0.7 9.1 68 example 2Comparative 65 11 77 12 17 0.6 8.7 75 example 3 Comparative 57 5 57 3833 0.7 10.1 48 example 4 Comparative 58 19 75 6 19 0.7 9.7 90 example 5Comparative 56 24 70 7 17 0.7 10.2 88 example 6

INDUSTRIAL APPLICABILITY

As has been described thus far, according to a porous honeycomb filterand a manufacturing method thereof of the present invention, a poroushoneycomb filter of this invention has a high collection efficiency forparticulates, or the like, and can prevent an increase in pressure lossdue to the plugging of pores, and particularly can exploit thecharacteristics thereof for diesel engines that use recent high-pressurefuel injection, common rails, etc.

What is claimed is:
 1. A porous honeycomb filter made from a materialcontaining cordierite, a pore distribution thereof being controlled, asthe primary crystalline phase, characterized in that said poredistribution is such that the volume of a pore with a diameter of lessthan 10 μm is 15% or less of the total pore volume, the volume of a porewith a diameter of 10 to 50 μm is 75% or more of the total pore volume,and the volume of a pore with a diameter of more than 50 μm is 10% orless of the total pore volume.
 2. The porous honeycomb filter accordingto claim 1, characterized in that the porosity of the honeycomb filteris 50 to 75%.
 3. The porous honeycomb filter according to claim 2,characterized in that the porosity of the honeycomb filter is 65 to 75%.4. The porous honeycomb filter according to claim 3, characterized inthat the honeycomb filter has a coefficient of thermal expansion of1.0×10⁻⁶/° C. or less at from 40 to 800° C.
 5. The porous honeycombfilter according to claim 2, characterized in that the honeycomb filterhas a coefficient of thermal expansion of 1.0×10⁻⁶/° C. or less at from40 to 800° C.
 6. The porous honeycomb filter according to claim 1,characterized in that the honeycomb filter has a coefficient of thermalexpansion of 1.0×10⁻⁶/° C. or less at from 40 to 800° C.
 7. A method ofmanufacturing a porous honeycomb filter using a ceramic raw materialcontaining a cordierite-forming raw material as the primary rawmaterial, said method comprising: forming a ceramic raw materialcontaining a cordierite-forming raw material as a primary raw material;molding the ceramic raw material into a raw molded article; drying theraw molded article to form a dried molded article; and firing the driedmolded article, wherein said cordierite-forming raw material contains 0to 10% by weight of kaolin and has a particle size distribution suchthat powder with a particle diameter of 75 μm or more accounts for 1% byweight or less of silica (SiO₂) source components.
 8. The method ofmanufacturing a porous honeycomb filter according to claim 7,characterized in that said cordierite-forming raw material contains 1 to10% by weight of said kaolin.
 9. The method of manufacturing a poroushoneycomb filter according to claim 7, characterized in that silica(SiO₂) source components except both said kaolin and said talc containat least one of quartz and fused silica.
 10. The method of manufacturinga porous honeycomb filter according to claim 7, characterized in thatsaid cordierite-forming raw material contains as alumina (Al₂O₃) sourcecomponents at least one of aluminum oxide and aluminum hydroxide. 11.The method of manufacturing a porous honeycomb filter according to claim10, characterized in that as said alumina (Al₂O₃) source component iscontained 15 to 45% by weight of aluminum hydroxide with a particle,diameter of 1 to 10 μm.
 12. The method of manufacturing a poroushoneycomb filter according to claim 10, characterized in that as saidalumina (Al₂O₃) source component is contained 0 to 20% by weight ofaluminum oxide with a particle diameter of 4 to 8 μm.
 13. The method ofmanufacturing a porous honeycomb filter according to 5, characterized inthat said cordierite-forming raw material contains 37 to 40% by weightof talc as a magnesia (MgO) source component.
 14. The method ofmanufacturing a porous honeycomb filter according to claim 13,characterized in that the particle diameter of said talc is 5 to 40 μm.15. The method of manufacturing a porous honeycomb filter according toclaim 7, characterized in that the ceramic raw material contains 1 to 4parts by weight of a foam resin with respect to 100 parts by weight ofthe cordierite-forming raw material.